Germany is full of great train rides, but one of the simplest, cheapest and most historic is the S-Bahn across Berlin, on the elevated section – Zoologischer Garten to Ostbahnhof and beyond – which cuts a swathe across the heart of the city. Ticking off backyards, allotments, housing developments, parkland, waterways, museum islands and government offices, the trains – deliberately retro in design – travel serenely across the face of the city, as they were always intended to do.

But the well informed traveller following this route will be on the alert, because this was once the most fraught of journeys, allowing west Germans to effectively cross the Wall and rumble across viaducts through the east, before touching ground in the west again with a sigh of relief. En route there was always a risk of a hijack, a kidnap, of getting involved in something and never getting out again.

When the Wall was erected in 1961 it made a nonsense of the public transportation network

This hole in the Iron Curtain dates back to the time when the Allied powers carved out their respective occupation sectors in Berlin. They paid little regard to actual urban layout, so the central district of Mitte, firmly in Soviet hands, became surrounded on three sides by west Berlin territory. Therefore when the Wall was erected in 1961 following the Soviet lines it made a nonsense of the public transportation network.

The result was that several lines which started off in west Berlin had to traverse what was now east Berlin in order to reach their terminus stations. These trains were permitted to enter but were not allowed to stop at intermediate stations, which become known as Ghost Stations.

They were however allowed to stop at Friedrichstrasse, even though it was on East German territory, because it was also the intersection point of west Berlin lines, and passengers had to change trains here under the scrutiny of very hostile guards. To keep the two worlds apart, the east German government created an elaborate maze of barriers and security checkpoints, separating the flow of citizens at each step of the way.

Because of the transport inter-section there was also a highly-controlled border crossing at Friedrichstrasse, and it became the place of numerous escape attempts of east Berliners trying to reach the west. The separate building created as a border crossing for west Berlin citizens became known as the ‘Palace of Tears’ because of the emotional partings that took place in front of it, and many a furtive passenger boarded one of the trains bound for the west, only to be hauled off again.

Also at Friedrichstrasse, the east Germans used an obscure service entrance to infiltrate agents into the western sector. The same passageway was used by members of the west German Communist Party and the west Berlin Socialist Party to pass from one country to the other without being checked or recorded.

All has been much cleaned up and rearranged since then, but as you rumble over the viaducts and look down on the cityscape, you might still feel the hairs prick up on the back of your neck.

Current Berlin S-Bahn network map and information.   Map of the network in 1961.